SSL_CTX_SET_INFO_CALLBACK(3SSL)

📦
version 4.0.3 · 14 versions
, in ubuntu stonking

💖 SSL_CTX_SET_INFO_CALLBACK 💖

okay bestie, welcome to the OpenSSL manual page for SSL_CTX_SET_INFO_CALLBACK (that's the 3SSL section, for all my section-heading girlies ✨). this is the info callback page and it's genuinely so useful, like it's giving backstage-pass-to-the-TLS-handshake energy 👑

✨ NAME ✨

SSL_CTX_set_info_callback, SSL_CTX_get_info_callback, SSL_set_info_callback, SSL_get_info_callback — handle information callback for SSL connections 🎀

no fr that's what they all do, four little functions, one whole vibe.

🌸 SYNOPSIS 🌸

#include <openssl/ssl.h>

void SSL_CTX_set_info_callback(SSL_CTX *ctx,
                               void (*callback) (const SSL *ssl, int type, int val));

void (*SSL_CTX_get_info_callback(SSL_CTX *ctx)) (const SSL *ssl, int type, int val);

void SSL_set_info_callback(SSL *ssl,
                           void (*callback) (const SSL *ssl, int type, int val));

void (*SSL_get_info_callback(const SSL *ssl)) (const SSL *ssl, int type, int val);

look at those function-pointer return types. yes ma'am, cursive ✍️💅. copy them exactly, i am not letting you retype them from memory.

💜 DESCRIPTION 💜

okay so, the setters and the getters, let's go one by one:

  • SSL_CTX_set_info_callback() — sets the callback function that you can use to obtain state information for SSL objects created from ctx, during connection setup and use. and here's the tea: the setting for ctx gets overridden by the setting for a specific SSL object, if one is specified. and when callback is NULL? no callback function is used at all. byeee 👋
  • SSL_set_info_callback() — sets the callback function you can use to obtain state information for ssl during connection setup and use. when callback is NULL, the callback setting currently valid for ctx is used instead (so it falls back, adorable). and ssl MUST NOT be NULL. like literally do not do that 🔥
  • SSL_CTX_get_info_callback() — returns a pointer to the currently set information callback function for ctx.
  • SSL_get_info_callback() — returns a pointer to the currently set information callback function for ssl.

that's it, that's the whole description, slay 💖

🌈 NOTES 🌈

so when you're setting up a connection and during use, it is possible to obtain state information from the SSL/TLS engine. when it's set, an information callback function is called whenever a significant event occurs, such as:

  • the state changes
  • an alert appears
  • an error occurs

the callback function is called as callback(SSL *ssl, int where, int ret). the where argument specifies information about where — like, in which context — the callback function was called. if ret is 0, an error condition occurred 😭. if an alert is handled, SSL_CB_ALERT is set and ret specifies the alert information.

🦋 the where bit-mask 🦋

where is a bit-mask made up of the following bits:

  • SSL_CB_LOOP — callback has been called to indicate state change or some other significant state machine event. this may mean that the callback gets invoked more than once per state in some situations. not me getting called multiple times 🙈
  • SSL_CB_EXIT — callback has been called to indicate exit of a handshake function. this will happen after the end of a handshake, but may happen at other times too, such as on error or when IO might otherwise block and nonblocking is being used.
  • SSL_CB_READ — callback has been called during read operation.
  • SSL_CB_WRITE — callback has been called during write operation.
  • SSL_CB_ALERT — callback has been called due to an alert being sent or received.
  • SSL_CB_READ_ALERT (SSL_CB_ALERT|SSL_CB_READ)
  • SSL_CB_WRITE_ALERT (SSL_CB_ALERT|SSL_CB_WRITE)
  • SSL_CB_ACCEPT_LOOP (SSL_ST_ACCEPT|SSL_CB_LOOP)
  • SSL_CB_ACCEPT_EXIT (SSL_ST_ACCEPT|SSL_CB_EXIT)
  • SSL_CB_CONNECT_LOOP (SSL_ST_CONNECT|SSL_CB_LOOP)
  • SSL_CB_CONNECT_EXIT (SSL_ST_CONNECT|SSL_CB_EXIT)
  • SSL_CB_HANDSHAKE_START — callback has been called because a new handshake is started. it also occurs when resuming a handshake following a pause to handle early data. 🫶
  • SSL_CB_HANDSHAKE_DONE — callback has been called because a handshake is finished. it also occurs if the handshake is paused to allow the exchange of early data.

and then, the lore:

⭐ RETURN VALUES ⭐

  • SSL_set_info_callback() does not provide diagnostic information. nothing. zero. it's giving silent treatment 💀
  • SSL_get_info_callback() returns the current setting.

🎀 EXAMPLES 🎀

here's the moment you've been waiting for. the following example callback function prints state strings, information about alerts being handled and error messages to the bio_err BIO:

void apps_ssl_info_callback(const SSL *s, int where, int ret)
{
    const char *str;
    int w = where & ~SSL_ST_MASK;

    if (w & SSL_ST_CONNECT)
        str = "SSL_connect";
    else if (w & SSL_ST_ACCEPT)
        str = "SSL_accept";
    else
        str = "undefined";

    if (where & SSL_CB_LOOP) {
        BIO_printf(bio_err, "%s:%s\n", str, SSL_state_string_long(s));
    } else if (where & SSL_CB_ALERT) {
        str = (where & SSL_CB_READ) ? "read" : "write";
        BIO_printf(bio_err, "SSL3 alert %s:%s:%s\n", str,
                   SSL_alert_type_string_long(ret),
                   SSL_alert_desc_string_long(ret));
    } else if (where & SSL_CB_EXIT) {
        if (ret == 0) {
            BIO_printf(bio_err, "%s:failed in %s\n",
                       str, SSL_state_string_long(s));
        } else if (ret < 0) {
            BIO_printf(bio_err, "%s:error in %s\n",
                       str, SSL_state_string_long(s));
        }
    }
}

copy that verbatim bestie, every brace, every %s, every ~SSL_ST_MASK. no cap 🧚

🔥 SEE ALSO 🔥

Copyright 2001-2020 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

and that's the whole page, you ate that 💅 this was version 4.0.3, dated 2026-09-29, and yes the manual page title really is SSL_CTX_SET_INFO_CALLBACK(3SSL) — go forth and log your handshakes, main character 🌟💖

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